The intestinal mucosa is the site of synthesis secretion, and turnover of many organ specific proteins. We have continued our studies on general protein turnover and have determined that lysosomal as well as bacterial proteases can effect turnover of brush border enzymes. In man pancreatic proteases can affect steady state levels of lactase as well as the previously demonstrated sucrase and maltase. An enteropancreatic secretin of pancreatic enzymes was looked for, but not found. The specific proteins studied include calcium binding protein, intrinsic factor-cobalamin receptor, and alkaline phosphatase. Dog calcium binding protein was purified and found to exist in a smaller (MW 19,700) and larger (MW 57,000) form. The smaller form could be produced by proteolysis from the larger one. The IF-Cb1 receptor has been purified 65,000-fold from dog ileum. It has a MW of about 200,000 and contains little carbohydrate. Alkaline phosphatase from rat intestine has been shown to be made in two independent forms, soluble and membrane-bound, neither of which is a precursor or product of the other. The uptake of the phosphatase from the serum is rapid and is mediated by the mannose receptor system.